1. Field of the Invention
The present invention generally relates to a liquid crystal display device, and more particularly to a liquid crystal display device which has a matrix electrode structure to drive n.times.m pixels.
2. Description of Related Art
JP-A-5-119746 discloses a liquid crystal display device with a matrix electrode structure. As the liquid crystal for the display, an anti-ferroelectric material is used. The anti-ferroelectric liquid crystal of this kind has at least one anti-ferroelectric state (a first stable state AF) and two ferroelectric states (second and third stable states F+, F-), and each of these states can be attained stably.
The liquid crystal display device disclosed in the above-mentioned publication displays picture images on the panel by sequentially scanning its scanning electrodes which constitute a matrix together with signal electrodes. A selection voltage for writing images in combination with a signal voltage supplied to the signal electrodes is sequentially supplied to the scanning electrodes, and then a holding voltage to maintain the written images is supplied to the scanning electrodes. The selection voltage is supplied to each scanning electrode with a predetermined phase shift. However, there are problems that the images may be displayed as ghost images and that moving images are difficult to be displayed in a good condition. This is because a response time for changing the state of the anti-ferroelectric liquid crystal from the ferroelectric state (F+ or F-) to the anti-ferroelectric state (AF) is more than 10 times longer than a response time for changing from AF to F+ or F-, and, accordingly, time required for switching images displayed becomes considerably long. In other words, displayed images are influenced by the optical response time of the anti-ferroelectric liquid crystal when they are eliminated, and, accordingly, the state of the liquid crystal immediately before application of the selecting voltage is different by pixel by pixel and luminance of each pixel may not be uniform even a same level of the selecting voltage is applied to pixels. This problem occurs not only in moving images but also in switching still images.
To solve the above-mentioned problem, some proposals have been made, for example, in JP-A-7-28432 and JP-A-7-43676. JP-A-7-28432 proposes to provide a response period to make the anti-ferroelectric liquid crystal change from the ferroelectric state to the anti-ferroelectric state in the selecting period. However, this driving method requires a longer time to scan one scanning electrode, because the selecting period is a total of both periods for writing images and for changing the state of the anti-ferroelectric liquid crystal from the ferro-electric state to the anti-ferroelectric state. Therefore, in the device having a large number of the scanning electrodes, moving images cannot be displayed properly. JP-A-7-43676 proposes to provide an eliminating period in which the anti-ferroelectric liquid crystal changes its states from the ferro-electric to the anti-ferroelectric between the selecting period and the holding period. This driving method enables to display the moving images in the device having a large number of scanning electrodes. However, because the level of the voltage applied in the eliminating period is zero, the response time from the ferroelectric state to the anti-ferroelectric state becomes longer, and, accordingly, the eliminating period has to be made longer. Therefore, there are such problems that the display luminance is low and that flicker appears when the display panel is driven by a low frequency. Also, in both driving methods disclosed in the above publications, the response of a particular pixel selected is influenced by image signals determining a display condition of other pixels to which the image signals are applied in an eliminating period before the selecting period for the particular pixel. This results in a phenomenon called a cross-talk in the longitudinal direction of the signal electrodes.